1. Field of the Invention
The present invention relates to an expansion valve integrated with an electromagnetic valve, in which the electromagnetic valve is disposed at a downstream side of the expansion valve and both are integrated. The present invention is suitably employed in, for example, an air conditioning apparatus for a vehicle, which has an air conditioning unit incorporating therein evaporators of a refrigeration cycle, disposed at a front side and a rear side, respectively, in a passenger compartment.
2. Description of the Related Art
A conventional air conditioning unit includes cooling evaporators respectively disposed on a front side and a rear side of a passenger compartment of a vehicle for independently performing an air conditioning control at the front side and at the rear side of the compartment. Each of the cooling evaporators is disposed in parallel to an expansion valve for decompressing refrigerant flowing into the evaporators.
In this refrigeration cycle, an electromagnetic valve is connected to the expansion valve in series and switches a flow of the refrigerant into the respective evaporators. When the electromagnetic valve is rapidly opened or closed, however, water hammer noise is liable to be generated. To solve this problem, JP-A-7-151422 proposes an expansion valve integrated with an electromagnetic valve which is disposed at a downstream side of the expansion valve, i.e., in a path at a low-pressure side through which gas and liquid two phase refrigerant flows. Accordingly, both of the electromagnetic valve and the expansion valve are downsized, and simultaneously, the water hammer noise generated when the electromagnetic valve is closed is reduced.
However, as a result from various studies and examinations of the above-described expansion valve integrated with the electromagnetic valve by the inventors, it turns out that the noise generated when the electromagnetic valve is opened cannot be reduced due to the following reasons.
That is, when the refrigerant is stopped by the closed electromagnetic valve not to flow into one of the evaporators in the refrigeration cycle, a temperature of the evaporator increases up to an ambient temperature (a room temperature). Therefore, a temperature of a temperature sensing bulb disposed at a refrigerant outlet side of the evaporator also increases up to the room temperature. In contrast, a pressure at a low-pressure side of this expansion valve lowers by the refrigerant circulating into the other evaporator (by an operation of a compressor). As a result, a force is applied to a valve body of the expansion valve to fully open the expansion valve. Accordingly, when the electromagnetic valve is opened in the sate where the expansion valve is fully opened, a large amount of the refrigerant, which has been stopped, starts to flow into the evaporator suddenly. As a result, there arises noise by the refrigerant flow and by sudden pressure drop at the downstream side of the expansion valve.
Therefore, the applicant of the present invention proposes, in U.S. application Ser. No. 08/884,758, another type of expansion valve integrated with an electromagnetic valve capable of effectively reducing refrigerant flow noise which is generated when the electromagnetic valve is opened. The expansion valve integrated with the electromagnetic valve includes a restriction path for decompressing and expanding high-pressure side refrigerant, a valve element for adjusting an opening degree of the restriction path, a valve element operating mechanism for moving the valve element, an outlet refrigerant path for supplying the refrigerant, which is decompressed an expanded in the restriction path, into an evaporator. The outlet refrigerant path is closed or opened by a valve element of the electromagnetic valve. When the valve element of the electromagnetic valve is closed, the valve element operating mechanism works based on the refrigerant pressure between the valve element of the electromagnetic valve and the restriction path to close a valve element of the expansion valve provided in the restriction path.
That is, the pressure at the upstream side of the electromagnetic valve becomes the high-pressure side pressure by the operation of the refrigeration cycle while the electromagnetic valve is closed. Then, the valve element operating mechanism can be operated utilizing the high-pressure side pressure to close the valve element of the expansion valve. Accordingly, when the electromagnetic valve is opened after that, a large amount of the refrigerant is prevented from suddenly flowing into the evaporator, so that refrigerant flow noise and the like do not occur when the electromagnetic valve is opened.
The inventors of the present invention further manufactured and studied the expansion valve integrated with the electromagnetic valve proposed in the previous application described above, and accordingly found out the following problem. That is, when the electromagnetic valve is closed, the space between the valve element of the electromagnetic valve and the valve element in the restriction path of the expansion valve is substantially sealed. When the sealed space is filled with liquid-phase refrigerant, the pressure in the sealed space can abnormally increase to, for example, more than 60 kg/cm.sup.2 in accordance with a rise in atmospheric temperature. The abnormal increase in the pressure may cause deformation and damage to the parts such as a diaphragm of the valve element operating mechanism, a diaphragm casing member, and the like.